Semiconductor dies are manufactured from wafers by fabricating, testing and dicing of the dies. Dies, also known as “chips”, contain the finished circuitry of semiconductor components, e.g. processors, memory circuits and others. Not all fabricated dies present on a wafer are operable and thus individual dies must be tested and defective dies discarded.
On wafer burn-in testing is one type of test typically used to separate good and bad dies. For the wafer tests, voltage busses Vcc and Vss are often fabricated over a protection passivation layer for the wafer. The protective layer is also selectively etched to expose Vcc and Vss conductive pads on the individual dies which are electrically connected to the Vcc and Vss voltage busses that run across the wafer. This bus and pad structure supplies power to the dies during the wafer burn-in tests. The Vcc and Vss voltage busses can be located in the street area between dies or over the top of dies covered with protective layer.
During wafer level testing, fuses are respectively associated with the dies and are used to isolate a die which is defective and draws excessive current from one or both of the Vcc and Vss busses. In this way, a die drawing excessive current during the on-wafer testing can be disconnected by a blown fuse from the busses and not affect the testing of other dies.
The wafer level testing is typically conducted in a furnace to temperature stress the dies during burn-in testing to check for defects. A series of predetermined voltages may also be applied to the dies during the burn-in test, through the Vcc and Vss busses, in an effort to detect dies which will not operate properly within design specifications under various temperature conditions. The fuses associated with each die are blown automatically when excessive current is drawn or manually when an over-current or latch up condition is detected within a die. (Latchup is a condition where the die circuits lock up and draws damaging levels of high current)
The fuses are important in isolating a defective die from other dies connected to the Vcc and Vss busses during die testing. Typically, sacrificial fuses are provided as part of the sacrificial Vcc and Vss bus structure over the dies or in the street areas between dies. Etching away sacrificial fuses from dies after burn-in complicates post burn-in identification of defective dies. Additional time is required to test each die for high current condition defects rather than a simple continuity check of a die fuse.
Another problem is that existing die processing and testing methods also do not adequately protect non-sacrificial on-die structures during subsequent etching of bonding pads used for electrical connection to the die. Extensive precautions and effort must be undertaken to avoid damaging non-sacrificial components when the sacrificial components are etched away.